Question For Rank Placements

If you lose but play really well how does that effect it versus winning and playing medorce/bad? Do only wins matter or performances/how much is the win vs performance weighted

I've got a tinfoil hat conspiracy theory that my performance in placements doesn't matter
throughout the years I've had placements where I've fully MVP'ed and won all 5, and placements where I've botted out and lost all 5, yet I always consistently get placed two whole ranks below where I was at the end of last season

When I first started the game, I was 5 stacked with a few friends (including a plat 3) and won 4/5 of my games in low gold lobbies. I ended up placing iron 1, where I was stuck for about 2 months.

So I guess that just goes to show that individual performance matters more than anything